31.08.2026
Smart Sauna and Remote Start: How to Safely Start Your Sauna from Your Phone
Smart sauna and remote start make it possible to begin heating your sauna from your phone, but they also raise an important question: how can you make sure the sauna is safe to start remotely?
What if a towel or another object has been left on the heater? Or what if someone enters the sauna room after you have already checked it?
With UKU 4.2, the user must check the sauna room before remote start is enabled.
Once the sauna has been confirmed as safe, the door sensor detects if the sauna door is opened, while other built-in safety features monitor the heating process.
Remote start is just one part of the smart sauna experience. For a broader look at remote control, sauna bookings, real-time alerts, and other app features, explore what’s new in the HUUM app.
Let’s take a closer look at how Remote start safety works, what the UKU sensors monitor, and why correct sensor placement matters.
Remote Start Safety: What It Is and Why It Matters
Remote start safety is designed to make remote sauna heating safer by requiring a physical check of the sauna room before remote start is enabled.
When you start the heater while you are at the sauna, you can first check that there is nothing on or near the heater that could create a fire hazard when heated.
When starting the sauna remotely, however, you cannot inspect the sauna room at that exact moment.
This is why the UKU control system includes the Remote start safety function, which is enabled by default.
It applies both when starting the sauna remotely right away and when using a scheduled booking.
The function does not inspect the sauna room for you. Before enabling remote start, you must make sure that there are no towels or other objects on or near the heater that could create a hazard when the heater is turned on.
Flammable materials must also remain outside the minimum safety distances specified for the heater.
You should also make sure that no one is inside the sauna room.
Once you have checked the sauna room, you need to confirm on the UKU control panel that the sauna is safe for remote start.
Confirming the Sauna Is Safe for Remote Start
Confirming the sauna is safe for remote start is done directly on the UKU control panel after you have checked the sauna room.
If the control panel is installed outside the sauna room, close the sauna door before confirming safety.
Press and hold the control panel button for about three seconds until the safety confirmation prompt appears. Select Yes.
If the control panel is installed inside the sauna room, confirm the safety on the control panel, leave the sauna, and close the door.
After successful confirmation, three gray dots appear on the control panel screen, indicating that the sauna is ready for remote start.
Confirming the safety does not start the heater. It simply enables the sauna to be started later from the HUUM app, either immediately or at a scheduled time.
If you select No or do not respond to the prompt, the system will not allow the sauna to be started from the HUUM app, either immediately or through a booking.
To confirm Remote start safety, press and hold the UKU control panel button for about three seconds until the safety confirmation prompt appears.
Confirming Safety Before Every Remote Start
Confirming safety before every remote start is not necessary as long as the SAFE status remains active.
Once you have confirmed that the sauna is safe for remote start, the SAFE status remains active until the sauna door is opened or power to the UKU main module is interrupted.
If the door is opened during heating, you will need to inspect the sauna room again and confirm that it is safe before the next remote start or scheduled booking.
If you start heating and then stop it without opening the sauna door, the SAFE status remains active and the sauna can be started remotely again later.
The Role of the Door Sensor in Remote Start
The role of the door sensor in remote start is to monitor whether the sauna door is open or closed.
If the door is left open, the control system prevents the heater from starting or stops heating if a heating cycle is already active.
If the door is opened after Remote start safety has been confirmed, the SAFE status is canceled.
Before the next remote start, you need to inspect the sauna room again and confirm that it is safe.
In the US installation instructions, the door sensor is a required part of the UKU 4.2 safety system.
Changing the Remote Start Safety Setting
Changing the Remote start safety setting is only possible when the heater is not heating.
Press and hold the control panel button to access the settings. Continue holding the button until the settings menu opens.
Then go to:
Safety Settings → Remote Start Safety: Enabled/Disabled
The Remote start safety confirmation can be disabled. However, doing so allows the sauna to be started remotely without first confirming on the control panel that conditions inside the sauna are safe.
For this reason, HUUM recommends keeping Remote start safety enabled when remote start is used.
Safety Goes Beyond Remote Start
Safety goes beyond remote start with UKU 4.2, as the control system continues to monitor the sauna after heating has begun.
An important part of this is the safety sensor, which is installed directly above the heater and monitors the temperature in that area.
The safety sensor also incorporates a thermal fuse. This is a hardware-based safety measure and does not depend on the mobile app.
In other words, UKU safety is not based on software alone: essential protective functions are also built into the control system hardware.
The Bench Sensor Measures Temperature and Humidity
The bench sensor measures temperature and humidity inside the sauna room and gives UKU information about conditions away from the direct heat of the heater.
The safety sensor and bench sensor have different roles. The safety sensor helps protect the sauna from overheating, while the bench sensor measures the temperature and relative humidity inside the sauna room.
When both sensors are installed, the temperature shown on the control panel comes from the bench sensor rather than the safety sensor.
Relative humidity measurement is particularly important when UKU is used to control a steamer. The system uses the humidity measurement to regulate the steamer according to the selected settings.
Sensor Placement Affects Measurement Accuracy
Sensor placement affects measurement accuracy because the temperature is not the same throughout the sauna room.
The air directly above the heater is usually hotter than elsewhere in the sauna. Ventilation openings and the proximity of doors, windows, and corners can also affect temperature readings.
Because the safety sensor and bench sensor serve different purposes, they also have different installation requirements.
The safety sensor must be installed directly above the heater, either on the wall or on the ceiling. Its exact location depends on the heater type and installation requirements.
Whenever possible, the bench sensor should be installed on the opposite side of the sauna from the safety sensor, where it is less affected by direct heat from the heater.
According to the UKU 4.2 US manual, the bench sensor must be installed:
- 5.9 in (150 mm) from the ceiling
- at least 19.7 in (500 mm) from ventilation openings
- at least 7.9 in (200 mm) from doors, windows, and corners
Correct sensor placement provides the control system with more accurate information about conditions inside the sauna and helps it regulate the heater accordingly.
For exact installation requirements, always refer to the UKU 4.2 user manual.
Example placement of the UKU safety sensor, bench sensor and door sensor in a sauna room.
Failure Detection Monitors How the Sauna Heats Up
Failure detection monitors how the sauna heats up and stops heating if the temperature does not rise sufficiently within a defined period.
The function is designed to detect abnormal heating behavior. For example, a sauna may heat too slowly if a door or window has been left open, the room is poorly insulated, the heater is undersized, or one of the sensors has been installed incorrectly.
With UKU 4.2, the required temperature rise depends on which sensors are installed.
If only the safety sensor is used, the temperature must rise by at least 72°F (40°C) within 60 minutes.
If both the safety sensor and bench sensor are installed, the temperature must rise by at least 36°F (20°C) within 60 minutes.
Failure detection applies when the sauna temperature is below 104°F (40°C) when heating begins.
If the required temperature increase is not reached, the control system shuts off the heater.
One possible reason for slow heating is heat loss. If you receive an insufficient temperature rise error, check that all sauna doors and windows are closed and that ventilation ports used for drying the sauna are also closed during heating.
This means the control system does more than monitor how hot the sauna currently is. It also checks whether the sauna is heating up as expected.
Overheating Pauses Help Protect the Sauna
Overheating pauses help protect the sauna by interrupting prolonged full-power heating at regular intervals.
UKU 4.2 uses a pausing mechanism after every 30 minutes of heating.
This is intended for situations where the sauna heater may be operating continuously at full capacity because the heater is undersized for the sauna room or the ventilation is not working as intended.
The pauses help reduce the risk of surfaces near the heater overheating.
Overheating pauses can be disabled in the settings, but HUUM recommends keeping them enabled.
If the heater repeatedly needs to run at full power for long periods, it is also worth checking whether the heater is correctly sized for the sauna and whether the ventilation is properly designed.
Convenience and Safety Go Hand in Hand
Convenience and safety go hand in hand when remote sauna control is combined with a physical safety check and UKU’s built-in safety features.
The UKU door sensor, temperature sensors, failure detection, and other protective functions do not replace the physical inspection of the sauna room. Instead, they help monitor conditions once the sauna has been confirmed as safe.
For the control system to work as intended, the sauna room must be properly designed, the sauna heater must be correctly sized, and the ventilation and sensors must be installed according to the applicable requirements.
This makes it possible to enjoy the convenience of starting your sauna from your phone while keeping the physical safety check an essential part of remote start.
